Calculate Torque Balance to Find the Angle of a String

[just.karl]

<a href="http://www.flickr.com/photos/just-karl/2407404197/" title="IMG_8600 by Karl W., on Flickr"><img src="http://farm3.static.flickr.com/2206/2407404197_18ab7a3497.jpg" width="500" height="317" alt="IMG_8600" /></a>

I have to find at what the angle of the string is using the torque balance equation.

W= 167.4grams
a= 49cm
b= 98cm
m= 100grams
The angle is 51 degrees based on the measurements during the lab, but I have to figure out how to do it using the torque balance equation.

What my guess is for the equation is Wga = mgbsin(angle

Am I going in somewhat of the right direction? Also how would I get the angle by it's self. Or how do you move sin if I do at all?

Thanks.

 

[just.karl]

sorry, I didn't put the diagram in right.

 

[Kurret]

yes, you are correct, now just solve for the angle. You need to use the inverse sinus function.

 

[just.karl]

When I punch it into my calculator I get error in the domain. It'd be sin^-1(Wa/mb correct?

 

[Kurret]

yes, and it works fine for me and i get 56 degrees. try again.

 

[just.karl]

if I calculate wa/mb then do sin_-1 it works out. Thanks

I have another question with this same diagram. "What are the predicted values of P_x and P_y?" Would it just be zero for both of them since there is no torque on it?